3781 has 4 divisors (see below), whose sum is σ = 4000. Its totient is φ = 3564.

The previous prime is 3779. The next prime is 3793. The reversal of 3781 is 1873.

3781 = 4² + 5² + ... + 22².

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 3781 - 2¹ = 3779 is a prime.

It is a super-2 number, since 2×3781² = 28591922, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (19), and also a Moran number because the ratio is a prime number: 199 = 3781 / (3 + 7 + 8 + 1).

It is a Duffinian number.

3781 is a lucky number.

It is a nialpdrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (3701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 81 + ... + 118.

It is an arithmetic number, because the mean of its divisors is an integer number (1000).

2³⁷⁸¹ is an apocalyptic number.

3781 is the 36-th hex number and also the 28-th centered decagonal number.

It is an amenable number.

3781 is a deficient number, since it is larger than the sum of its proper divisors (219).

3781 is a wasteful number, since it uses less digits than its factorization.

3781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 218.

The product of its digits is 168, while the sum is 19.

The square root of 3781 is about 61.4898365586. The cubic root of 3781 is about 15.5788558601.

It can be divided in two parts, 3 and 781, that added together give a square (784 = 28²).

The spelling of 3781 in words is "three thousand, seven hundred eighty-one".